T-even and T-odd bacteriophages carry genetic information for the synthesis of specific tRNA species; the function of these viral tRNAs in the replicative process is not well understood. We have detected some 18 different T5 tRNA species in extracts from T5 infected cells and have mapped their physical location in T5 DNA. The present map indicates that the T5 tRNA structural genes are clustered in the C-segment of T5 DNA within a total length of 13,800 nucleotides. Our primary objective is to refine the tDNA map so that the position of the individual tRNA genes may be precisely ordered in the T5 chromosome. Techniques for isolating the tDNA-containing C-segment have been partially effected. We expect to use this C-segment DNA for mapping and for studying the transcription of the tRNA gene clusters, in vitro. Other studies will be undertaken to define the process of T5 tRNA maturation and the role played by these transfer RNAs in the synthesis of T5 proteins.